This invention relates to a processing method of resistless, maskless electroless, 3-dimensional plating of an ink-jet print head, and a production method thereof.
Electroless plating is depositing a continuous film of metal by controlling reduction and oxidation reaction which occurs between metallic salts and reducing agents in a plating bath. By electroless plating, a film of metal, alloy, compound, or composite can be formed onto an electrically non-conductive surface.
Eelectroless plating is capable of conducting metal deposition without electric power. But, before electroless plating, plating catalyst must be absorbed onto a substrate to initiate metal deposition. Otherwise, the electroless plating cannot start.
After starting, already deposited metal itself can work as a self catalyst for further plating.
An electroless plating can coat a metallic layer onto a non-conductive substrate which has previously been subjected to a suitable pre-processing, such as washing, etching and catalyst absorbing, and an uniform metallic film can be deposited on any substrates whatever shape they may have. Usual electroless plating metal is nickel, and can be deposited onto a various kind of substrates, including metal, plastic, ceramic, and other non-conductors. Because electroless plating is capable of depositing a metal layer onto any surface, regardless of their conductivity and even inside wall of a small hole, it is widely used in a electronic industry, for example, in a circuit patterning of a printed wiring board, contact point of a connector, a semiconductor device, a package of a ceramic-metal-integrated circuit, a connector shell made of aluminum, a lead frame, formation of an electrode of an ink-jet print head, etc.
In particular, regarding an ink-jet print head, it can be cited, a piezo type ink-jet print head which jets inks from an ink chamber by a piezo ceramic actuator, attached to an ink chamber, through the application of an electric signal to an electrode of a piezo ceramic. Further, there is another type of piezo ink-jet print head which is called share-mode print head.
The share mode print head have many minute ink channels inside a piezoelectric ceramic itself and metal is selectively deposited onto a partition wall between the channels as an electrode.
By applying an electric signal to electrodes between a wall, share-mode deformation of the partition wall occurs and compress the ink inside the channel and ejects a droplet from the channel.
Ink-jet print head have to eject a droplet from each channel independently. But electroless plating deposits a metal film onto a whole surface evenly, so either masking before plating or removing unnecessary metals after plating, is inevitable, to separate electrode and wiring, in each channel.
In a print head, we must build both electrode pattern to actuate piezo ceramic channel and wiring pattern to connect between electrode and control circuit, simultaneously by electroless plating. The Patterning technology is very important for an ink jet print head.
Usual patterning technology is as follows, coat of a photoresist is conducted onto a substrate and UV is irradiated through an appropriate mask. After developing a pattern image, metal is deposited, onto a portion which is not masked.
As for ink jet print head, head size is very small and has many minute ink channels, and also, 3-dimensional wiring is required. Recently, channel width is approaching less than 50 xcexcm, and channel numbers are increasing over 500, and also, an electrode pattern must be built inside and a wiring pattern must be built outside of the channel, simultaneously by electroless plating. The usual patterning method using photoresist and mask is not adequate for ink jet print head due to its small size and a complex 3-dimensional structure.
Laser pattering is most suitable for ink jet print head. This is a resistless, maskless, 3-dimensional pattering.
Laser pattering technology of print head is described in the publications of Japanese Tokkaihei H8-300667 and H9-10976 and WO 00/29217. There is cited a method in which a pattering of an electrode and wiring is accomplished by evaporating a metal deposited in an unnecessary portion of a print head, by selective application of a high-energy laser beam.
As described in the patents, in the conventional technology, separation of an electrode and wiring is accomplished through evaporation of unnecessary metal film by a laser beam, but nickel is a very hard metal and has high melting temperature, therefore, high energy density laser beam is required, thus thermal shock and thermal distortion occur in the piezoelectric ceramic, the piezo-electrical properties is very sensitive to elevated temperature, and its performance is easily deteriorated by heat and also there is a possibility of damage in a print head.
Further, the high energy laser beam, requires a high-output and high-priced apparatus. Moreover, there is a possibility that the metallic film evaporated by high energy laser beam, have a tendency to redeposit around the surroundings, and may produce defects due to redeposited debris, in the final electrode and wiring, resulting in a short circuit.
This invention was performed in view of the above-mentioned actual situation, and its first object is to provide a processing method of a resistless, maskless and 3-dimensional electroless plating which is capable of forming a plating pattern having no defect at low cost without deteriorating both piezo-electrical and physical properties and further, without producing any damage in a head.
Its second object is to provide a new laser pattering method which evaporates plating catalyst, instead of plated metal. The former requires one-tenth energy of the latter, so undesirable heat shock, and debris formation can be minimized.
It can provide an ink-jet print head which has an electrode and wiring pattern, having no defect, at low cost without deteriorating both piezoelectric and physical properties and further, without producing any contamination due to debris in a head, and the method of manufacturing it.
Its third object is to provide a new UV pattering method which oxidize plating catalyst, instead of evaporation.
The former requires much lower energy, no undesirable heat shock, and no debris formation can be expected. It can provide an ink-jet print head which has an electrode and wiring pattern, having no defect, at low cost without deteriorating both piezoelectric and physical properties and further, without producing any damage in a head, and the method of manufacturing it.
For the purpose of solving the above-mentioned problems and accomplishing the objects, this invention was made to have any one of methods described in the following.
(Method 1): A processing method of electroless plating characterized in that a catalytic material for electroless plating is absorbed onto a surface of a piezo-electric ceramic, then a laser beam is selectively applied to this ceramic, finally, processing of electroless plating is applied to this ceramic, a metal layer is formed on the portion to which the laser beam has not been irradiated and a metal layer is not formed on the portion to which the laser beam has been irradiated.
To separate the electrode and wiring between channels, evaporating a catalyst, instead of metal, much lower laser power is needed, so much lower thermal damage and much lower debris can be expected. Because, the amount of catalytic material contained is only xcexcg order palladium, but the amount of electrode material contained is mg order nickel.
According to the method 1, prior to electroless plating, the substrate with catalyst has already been selectively irradiated by laser beam, a plating pattern having no defect can be formed at a low cost without deteriorating the piezoelectric and physical properties and further, without producing any damage and contamination in a print head.
(Method 2): A processing method of electroless plating characterized in that a catalytic material is absorbed onto a surface of a substrate, a photochemical reaction is made to occur selectively in the catalyst, then, processing of electroless plating is applied to this substrate, a plating layer is formed on the portion in which the photochemical reaction has not occurred, and a plating layer is not formed on the portion in which the photochemical reaction has occurred. Plating catalyst, such as palladium, can be deactivated by oxidation with ultra violet beam, instead of evaporation.
According to the method 2, by carrying out processing of electroless plating on a substrate with catalytic material absorbed thereon in which a photochemical reaction has been made to occur selectively. Because requisite energy of oxidation is much smaller than evaporation, no thermal damage, no debris can be expected, and, also, UV beam is more easy to handle than laser beam. The plating pattern having no defect can be formed at a low cost without deteriorating the piezoelectric and physical properties and further, without producing any damage in a head.
(Method 3): The same process as the method 1 or 2, except during plating, the substrate is picked up from the plating bath as soon as a thin metallic layer emerges, and to remove the trace amount of residual catalyst from the substrate, the substrate is washed by water and/or chemical etched. After washing thoroughly by water. The substrate is put into the bath, again, to resume the plating. Because already deposited metal works as a catalyst, so plating can continue.
We noticed that plating thickness less than 5 xcexcm, we can get a defect free pattern with method 1 or 2. But more than 5 xcexcm, undesirable metal sometimes deposits due to the trace amount of residual catalyst.
According to the method 3, by stopping the plating at the timing when a thin metallic layer has deposited and removing the residual catalytic material by washing and/or chemical etching, as the remaining catalyst is thoroughly eliminated, formation of a plating layer by deposition is suppressed completely, even after plating process is resumed. But, in the portion where a plating layer has already been formed, the plating layer itself act as catalyzer, plating continues and thick plating layer, more than 5 xcexcm, can be formed.
A method of manufacturing an ink-jet print head as set forth in the method 1, characterized in that the aforesaid laser beam is a pulse oscillation laser beam.
Aforesaid laser use a pulse oscillation laser beam, and by applying a light beam with a high energy density for a short time, it is possible to limit a thermal influence produced by the irradiation within a very narrow range.
A method of manufacturing an ink-jet print head as set forth in the method 1, characterized in that the irradiation by the aforesaid pulse oscillation laser beam is repeated two times or more on the same place.
In the case where a part remains to which the action of the laser pulse has not been given by an irradiation of only one time, the repeating of irradiation makes the action of the laser pulse certainly effective.
A method of manufacturing an ink-jet print head as set forth in the method 1, characterized in that the aforesaid pulse oscillation laser beam is a Q-switched laser beam.
According to the method 1, it uses a Q-switched laser beam, and because the Q-switched laser beam has a higher peak value and a narrower pulse width, in the case where a part remains to which the action of the laser pulse has not been given by an irradiation of one time, the action of the laser pulse can be made certainly effective by repeating irradiation; further, the action of the laser beam acts only on the outer layer portion, and the heat diffusion to the surrounding becomes less; therefore, it is possible to suppress the thermal influence and damage by the laser beam to a minimum limit.
A method of manufacturing an ink-jet print head as set forth in the method 1, characterized in that the aforesaid pulse oscillation laser beam is a Nd:YAG laser beam.
According to the method 1, by using a Nd:YAG laser beam, the laser device is made small-sized and has a high efficiency, and the convergence of the beam is good; therefore, it is very suitable.
A method of manufacturing an ink-jet print head as set forth in the method 1, characterized in that the aforesaid pulse oscillation laser beam is the second harmonic of a Nd:YAG laser.
According to the method 1, by making the pulse oscillation laser beam the second harmonic of a Nd:YAG laser, the wavelength is 532 nm, which is a half of, and shorter as compared to the wavelength of the basic wave 1.06 Mm, the convergence of the beam is better as compared to the basic wave, and it is a visible beam; therefore, it is easy to adjust the position of the irradiation by the laser beam to a minute portion, and also it is easy to do it exactly.
A method of manufacturing an ink-jet print head as set forth in the method 1, characterized in that the aforesaid pulse oscillation laser beam is the third harmonic of a Nd:YAG laser.
According to the method 1, by making the pulse oscillation laser beam the third harmonic of a Nd:YAG laser, although it is disadvantageous as compared to the second harmonic of a Nd:YAG laser in the sense that it is invisible because it is an ultraviolet ray, the convergence of the beam is better than the second harmonic owing to the wavelength being shorter, and generally speaking, it can be expected that the absorption ratio by a piezoelectric substance is higher than the second harmonic.
A method of manufacturing an ink-jet print head as set forth in the method 2, characterized in that, in the aforesaid processing of electroless plating, ultra violet beam is available, instead of laser beam. Although UV has less power than laser, UV is used to oxidize the catalytic material instead of evaporation. To make a thin metallic patterns, for example less than 1 xcexcm, UV is available and gives a satisfactory results. UV has no thermal damage and make no debris and also UV is more easy to handle, and less expensive than laser.
A method of manufacturing an ink-jet print head as set forth in the method 3, characterized in that, in the aforesaid processing of electroless plating, deposition process in plating is divided into a plurality of stages, and a residual catalytic material in the portion where electrode is not formed, is removed by water washing and/or chemical etching in an intermediate process between the stages.
According to the method 3, in order to prevent that, in the case where the catalytic material is not completely removed, if plating is continued for a long time to obtain a sufficient film thickness of plating, for example more than 5 xcexcm, sometimes a plating layer by deposition is also formed on a portion to which a laser beam has been applied, plating is once stopped at the timing when a thin plating layer by deposition, less than 1 xcexcm, is formed on a portion where no laser beam has been applied, and the catalytic material is removed again, by water washing and/or chemical etching. As residual catalytic material on the laser-irradiated portion has been removed thoroughly, formation of a plating layer by deposition is suppressed completely, even after plating is resumed. Nickel can work as a catalyst, so, in the non-irradiated portion, on which formation of a Ni plating layer has already been made, continues to grow without a catalyst.
A sufficiently thick plating layer, more than 5 xcexcm, can be formed.